It is well known to make open-ended type orthotic devices including spinal, knee, and thigh braces and closed-ended type prosthetic devices by vacuum forming a thermal plastic sheet on a positive mold. The mold is configured for surface suction of the thermal plastic sheet into conformance with the contours of the mold surface as vacuum is applied to the mold from a vacuum source connection at one end of the mold.
The prior art technique for making the mold provides a shaft, to which is applied a bulk material that can be formed to match the profile of the subject for which a brace is to be made, the shaft ends protruding from the mold end or ends for handling. In one known method, a heavy foam or plaster body is cast as a male mold or mold blank onto a solid shaft so as to encapsulate the shaft and lock the shaft in a non-rotating manner within the mold, the shaft extending out at least one end for handling and fixed or rotating support. For brace making, the shaft is inserted into the throat of a vacuum source, and into a chuck for support and rotation. An orthotic brace or prosthesis is then molded by wrapping thermoplastic sheet material around the mold, extending over the shaft end to and around the vacuum source so as to form an envelope of the thermoplastic sheet material over the mold. The brace is cooled for hardening, and removed from the mold by known methods. The mold is then typically stored for making similar size braces, with or without recontouring of the surface.
In this method, the shaft is committed for the life of the mold and is recoverable only when the mold body is destroyed. Further, a relatively large vacuum pressure is required during the vacuum forming process under this method. The shaft is a relatively expensive component of the mold, compared to the mold body.
In another known method, a plenum or chamber structure of some sort is applied to or fabricated on a hollow shaft or mandrel as a first step. The shaft sidewall is predrilled with small ports along the center section to permit a vacuum source connectible to the shaft end to draw a vacuum within the plenum. A heavy foam or plaster body is then cast as a male mold or mold blank onto the shaft and plenum assembly so as to encapsulate the plenum and lock the shaft in a non-rotating manner within the mold, the shaft ends extending out both ends of the mold for handling and fixed or rotating support. Multiple small diameter holes are drilled through the body of the mold to provide air passageways from the surface to the chamber or plenum. Thermoplastic sheet material is wrapped around the mold body, and with vacuum applied to the shaft end, the sheet material is drawn into conformance with the contours of the mold body. The mold is then stored for reuse for similar size braces, with or without re-contouring of the surface.
This method increases the efficiency of the vacuum forming process, vacuum pressure is significantly reduced extending the life of the vacuum source equipment. However, in this method, as in the prior method, the shaft is committed for the life of the mold and is recoverable only when the mold body is destroyed. As in the above method, the shaft and plenum component is a relatively costly part of the mold. The chamber or plenum portion is usually destroyed with the mold body and not recoverable; only the bare shaft being recoverable for reuse.
In yet another known method, typically a foam mold blank is preformed according to various sizes within which a center hole is bored out to accept the exact shape of a milling machine mandrel. A one or two piece solid shaft mandrel is inserted into the preformed hole in the foam blank, securing it for chucking in a milling machine and milling a surface contour according to a CAD/CAM program so as to create the desired mold. The subsequent vacuum forming process for making a brace is similar to the first prior art technique described above where the shaft end is inserted in the throat of a vacuum source connector flange and chucked for rotation. The thermoplastic material is arranged wrapped by rotation of the mold so as to cover the mold and to extend from the mold to the vacuum source throat to connect the envelope to the vacuum source. The brace is removed as usual. However, in this latter method, the solid shaft milling machine mandrel is removable and reusable, and the mold is storable for reuse without the shaft.
A production brace making operation, commonly called central fabrication, requires the accumulation and use of a large library of molds of varying sizes, in order to provide quick response to medical requirements for spinal braces. Typically, upon receipt of a brace order, a same or similarly sized mold is selected from the library quickly reconfigured to conform to the patient's measurements and used to make the new brace. A new mold is made up when there is no existing mold that can be used as is or can be easily modified or re-contoured to satisfy the requirement, or when a brace is fabricated according to a digitized cast of the patient, which is not readily associated with the traditional format for characterizing and cataloging mold profiles.
Useful context for understanding the art and the invention may be obtained from the following disclosures; U.S. Pat. No. 3,871,367, U.S. Pat. No. 4,688,558, U.S. Pat. No. 4,820,221, and U.S. Pat. No. 5,074,288.